1. Field of the Invention
The present invention relates to methods and apparatus for transmitting power setting information in a downlink Physical Downlink Shared Channel (PDSCH) in a communication system.
2. Description of the Related Art
This application, pursuant to 37 C.F.R. §1.57, incorporates by reference the following publications:    [1]. “Chairman's notes”, 3GPP RAN WG1#51, November 2007, Jeju, Korea;    [2]. R1-075077, “Way-forward on Data Power Setting for PDSCH across OFDM Symbols”, Samsung, LGE, Nortel, Qualcomm, etc., November 2007, Jeju, Korea;    [3]. R1-080047, “Further Discussion on Data Power Setting for PDSCH”, Samsung, January 2008, Seville, Spain;    [4]. R1-081600, “Draft LS on information about RAN1decision regarding downlink power settings”, Nokia, Shenzhen, China;    [5]. 3GPP TS 36.213 Standard, Version 8.3.0; and    [6]. U.S. Provisional Patent Application Ser. No. 60/963,681, entitled “Pilot boosting and traffic-to-pilot ratio estimation in a wireless communication system”, filed on 7 Aug. 2007.
In RAN1#51 meeting in Jeju, November 2007[1][2], it was agreed, in order to enable the efficient power and bandwidth utilization at the eNodeB (i.e., base station) for all Orthogonal Frequency Division Multiplexing (OFDM) symbols but at the same time to minimize the signaling or estimation efforts for the data-to-reference signal (RS) Energy Per Resource Element (EPRE) ratio, that:
For each UE, the Physical Downlink Shared Channel (PDSCH)-to-RS EPRE ratios among resource elements (REs) in all the OFDM symbols containing RS are equal, and are denoted by P_A,
For each UE, the PDSCH-to-RS EPRE ratios among REs in all the OFDM symbols not containing RS are equal, and are denoted by P_B,
For each UE, P_A and P_B are potentially different due to different PDSCH EPRE,
The ratio between P_A and P_B is known at the UE. This ratio can be derived from the signaled RS boosting value, and from other signaling that is needed to derive this ratio.
It can be noted that the power available from each antenna port for subcarriers other than the reference signals, such as data subcarriers, vary from OFDM symbol to OFDM symbol. Keeping the power level equal across antennas on these subcarriers results in inefficient use of power because power level is limited to the minimum power level available from a given antenna port even though other ports may have extra power available. Likewise, keeping the power level the same across OFDM symbols on these subcarriers also results in inefficient use of power because power level is limited to the minimum power level available in one OFDM symbol although other OFDM symbols may have extra power available. Another solution could be to puncture some data subcarriers in OFDM symbols containing pilot signals in order to keep the power level the same across the symbols. This approach, however, may result in waste of subcarrier resources thus degrading system performance and capacity.